Many electronic devices, such as analog optical sensors, require a stable source optical energy. Thermoelectrically-cooled lasers have typically been used as sources of stabilized optical energy. Recent developments in the field of low-cost, high-intensity, super-luminescent LEDs, however, have made it desirable to use these types of devices in lieu of lasers in some applications.
The intensity of the optical energy generated by an LED, however, typically varies with the temperature of the LED. LEDs can be required to operate over temperature ranges as great as, or greater than −40° C. to +70° C. For example, the output intensity of certain types of surface-mount LEDs can fluctuate by as much as ten percent when the temperature decreases from ambient to about −40° C., or increases from ambient to about +70° C. Moreover, the output intensity usually varies as the LED ages. For example, the output intensity of certain types of LEDs can decrease over the operational life of the LED by as much as 27 percent.
Optical signals, in general, are usually monitored by tapping a relatively small, predetermined fraction of optical energy from the optical fiber carrying the signal. For example, a tapping fiber may be wrapped around and fused with the optical fiber carrying the signal. Alternatively, the optical fiber carrying the signal may be sharply bent so that a fraction of the optical energy escapes from the optical fiber. It is believed that the ratio of the tapped optical energy to the optical signal can vary by ten percent or more using each of these techniques. Stabilizing the intensity of the optical output of an LED, it is believed, requires measurement of the intensity with an accuracy of about one percent or better.
Consequently, an ongoing need exists for a system and method for providing optical energy of stabilized intensity using an LED.